Facebook announced a "crusade" against the Russian "Troll factories"

Addressing a major intelligence conference in Washington, Warner called "the tip of the iceberg" Facebook's revelation that it had tracked thousands of the ads to a Russian company linked to a so-called, Kremlin-directed "troll farm" that spread Russian propaganda. Emily Horne, a Twitter spokeswoman, declined to comment.

The fake accounts were discovered during a company review of ad buys that was spurred by a broader investigation the company initiated into Russian meddling after the election, Stamos said. The company hasn't disclosed the nature of the more than 3,000 ads that ran, and a spokesman wouldn't say what USA states they ran in, what they promoted or how many people they reached.

"That would not be the jurisdiction of our committee", the senator from North Carolina said.

USA intelligence agencies say there was an extensive Russian cyber-influence operation during the 2016 election campaign aimed at helping Mr Donald Trump, a Republican, defeat Democrat Hillary Clinton. "And if, in fact, there was foreign money that went into advertising in US elections, that's a Justice Department thing to look at, it's an FEC question, because foreign money can not be used on behalf of elections". "So they - they, and Twitter and others - we need a lot more answers". As recently as July, the company told CNN that it had "seen no evidence that Russian actors bought ads on Facebook in connection with the election".

Watchdog group Common Cause on Thursday filed a complaint with the U.S. Justice Department and the Federal Election Commission alleging that unknown foreign nationals made expenditures during the election in violation of American election law.

The dollar amount of ad spending identified by Facebook is an infinitesimal amount compared to the total amount of advertising spending during the election. Other ads fall into a legal gray area.

Television has been the backbone of political advertising for decades, and local USA broadcasters are required to disclose a wealth of details about the cost and schedules of commercials.

Online advertising offered by Facebook and other platforms such as Twitter and Alphabet Inc's Google, though, often targets narrow, carefully constructed audiences based on factors such as age, political preference or interests.

Facebook also said it was continuing its investigation into possible nefarious activity.

The U.S. presidential election has put the social-media company under increased scrutiny and forced it to consider its role in society, and Chief Executive Officer Mark Zuckerberg's thinking has evolved.

If Russia were found to have used front companies or loosely regulated US nonprofit groups to hide the source of funding while spreading fake or harshly critical news about Clinton over Facebook, then investigators would want to know whether any were targeted to swing states or districts crucial to Trump's upset victory.

Stamos noted that earlier this year, Facebookannounced improved technology for detecting fake accounts, as well as other actions to curb the flow of misinformation over its network.

"That's just not the case with digital", said Ken Goldstein, a professor at the University of San Francisco who studies political advertising.

Since then, the site and other social media competitors like Twitter have been forced to put out dozens of fires linked back to Russian Federation.